WASHINGTON — Baltimore's computer network that supports emergency calls was hacked this past weekend and suffered temporary disruption that forced city officials to resort to manual operations to handle calls, the city mayor's office said.

A "limited breach" affecting Baltimore's computer-assisted dispatch system, which is used to support and direct 911 and other emergency calls, was identified Sunday morning, according to Frank Johnson, Baltimore's chief information officer.

The disruption was the second cyber attack on a major U.S. city within the past week, coming just days after Atlanta was struck by a widespread ransomware attack that interrupted bill collection services, downed the airport's wireless internet and impeded other city services. A senior U.S. cyber security official said there were no indications the two attacks were related.

During the Baltimore outage, details of incoming callers seeking emergency support were unable to be relayed to dispatchers electronically and instead had to be manually managed by call center support staff, Johnson said.

He said the impacted computer server was isolated and taken offline to mitigate the threat and the computer-assisted dispatch system was fully restored by early Monday morning, about 17 hours after the issue was identified.

"These critical services were not impacted nor disrupted at any time, as they were temporarily transitioned to manual mode," Johnson said in a statement.

A spokesman for the mayor's office said the 911 dispatch system itself was not hacked. He declined to say if the city had identified any suspects behind the breach, whether any information was stolen from its systems or if other city services had been recently targeted by cyber attacks.

He added: "This is an active investigation. Getting into further details could compromise the investigation."

An FBI spokesman told the Baltimore Sun that the bureau was aware of the breach and providing technical assistance. The regional FBI office in Baltimore could not be immediately reached for comment.